Validation - two columns in a tabular form don't have same value in the same row

Hello,

             In a application, in a tabular form, the column1 can't have the same value of the column2 in the same row.

             Example:

                            Column1               Column2

                                 X                           X                        --> error message

                                 X                           Y                        --> OK

             I would wish that when I clicked the submit button, an error message appear if the values in column1 and column2 are equal in the same row of the table.

            How can I do this?